DESCRIPTION: The proposed research examines the intracellular signaling pathways in cerebellum Purkinje cells implicated in the initiation of long-term depression (LTD)by the conjunctive activation of the climbing fibers (CFs) and the parallel fibers (PFs)excitatory inputs. The specific hypothesis that will be tested is that the associative induction of LTD arises from a convergence between two intracellular signaling pathways, IP3 and calcium ions. More specifically, LTD is induced after CFs raise intracellular calcium sufficiently to permit PF- generated IP3 to release additional calcium from the intracellular stores within the postsynaptic spines of the Purkinje cells. The proposal has four specific aims to investigate: 1)the role of metabotropic glutamate receptors (mGluR)in PF signaling; 2)the role of calcium from IP3- sensitive internal stores in the induction of LTD; 3)the regulation of calcium release from IP3 sensitive stores by calcium levels; and 4)if LTD occurs after CFs raise intracellular calcium levels sufficiently to permit PF-generated IP3 to release more calcium from intracellular stores. The investigators seek to achieve these objectives through a series of experiment using rat cerebellar slices. The applicant's expertise with whole-cell recordings, ion imaging, confocal microscopy, and localized flash photolysis will be applied in these experiments.